Inorganic materials that have unusual structures often exhibit interesting chemical and physical characteristics which find extensive applications in diverse fields. For example, inorganic molecular sieves are porous crystalline structures comprising a solid three-dimensional framework with interconnected internal cavities or pores. Applications for these materials include ion, molecule, and gas separations; molecule and gas sensing; ion-exchange; and catalysis, among others.
Ordered porous manganese-based octahedral molecular sieves (OMS) constitute an exemplary class of molecular sieves. These materials have one-dimensional tunnel structures and unlike zeolites, which have tetrahedrally coordinated species serving as the basic structural unit, these materials are based on six-coordinate manganese surrounded by an octahedral array of anions (e.g., oxide). The OMS framework architecture is dictated by the type of aggregation (e.g., corner-sharing, edge-sharing, or face-sharing) of the MnO6 octahedra. The ability of manganese to adopt multiple oxidation states and of the MnO6 octahedra to aggregate in different arrangements affords the formation of a large variety of OMS structures.
Many commercial applications have traditionally used molecular sieves in the form of granules or pellets. Recently, films or membranes of molecular sieves have gained considerable importance as alternatives to granules or pellets. However, suitable inorganic oxide-based materials are difficult to prepare as films or membranes owing to their brittleness and poor mechanical properties. A variety of molecular materials, mostly organic polymers, have been found to be suitable for use as membranes. However, organic polymer membranes have relatively short service lives because of their sensitivity to solvents and low stability at high temperatures.
There accordingly remains a need in the art for new methods of preparing inorganic oxide-based molecular sieve films or membranes because of their superior thermal and chemical properties to organic polymers. It would be particularly advantageous if such methods could eliminate or result in decreased brittleness. It would be further advantageous if such methods could result in increased mechanical properties for processing the films or membranes.